The spatial and stratigraphic variations of upper Holocene and upper Quaternary sediments in the Colombia Basin reflect the terrigenous influx from South America and Panama. Calcium carbonate, composed of foraminifers and coccoliths, accumulates uniformly across the basin and is modified by terrigenous dilution and carbonate dissolution which reflect bathymetry. Glacial sediments of the Colombia Basin are lower in carbonate, have higher total accumulation rates, and thicken toward the continental margin in comparison to interglacial sediments. Carbonate accumulation is relatively constant between glacial and interglacial intervals, whereas clay accumulation greatly increases.
The primary cause of carbonate variation in Colombia Basin sediments is the terrigenous influx due to rapid erosion of shelf and upper slope sediments during eustatic lowering of sea level. This relationship should be true for most marginal basins and much of the Atlantic Ocean. This mechanism for variation of sediment composition implies that the carbonate record reflects not only climatic and ice-margin fluctuations but also changing erosional and depositional environments.